This invention relates to a high frequency amplifier circuit for producing an amplified output signal with automatic level control (ALC). The amplifier circuit is typically a radio frequency amplifier circuit and is particularly useful in a portable radio communication device.
The amplifier circuit comprises a high frequency output amplifier supplied with a bias voltage for amplifying an amplifier input signal into a circuit output signal which is the above-mentioned amplified output signal and is automatic level controlled in the manner which will presently be described. A high frequency input amplifier device is connected to the output amplifier and is for amplifying a circuit input signal into an intermediate amplified signal to deliver the intermediate amplified signal to the output amplifier as the amplifier input signal. Supplied with the circuit output signal back from the output amplifier, the input amplifier device makes the circuit output signal have a predetermined output level. In this manner, the automatic level control is carried out in the amplifier circuit comprising the input amplifier device and the output amplifier.
It is to be noted here that the circuit input signal has a variable input level. The amplifier input signal of the output amplifier has a gain controlled level. The input amplifier device may consist of a single high frequency input amplifier for producing the intermediate amplified signal. Alternatively, the input amplifier device may additionally comprise at least one high frequency intermediate amplifier connected to the input amplifier to produce the intermediate amplified signal for delivery to the output amplifier.
The amplifier circuit is naturally put into operation by electric power. When used in a portable radio communication device, the amplifier circuit is supplied with the electric power usually from a battery unit. The input amplifier device is supplied with a portion of the electric power as an input amplifier power. The output amplifier is supplied with another portion of the electric power as an output amplifier power. The amplifier circuit is kept in operation with a total power consumption of the electric power and is supplied with the electric power with a certain supply current value.
The power consumption should be kept as little as possible. It is therefore desirable to make the total power consumption have an optimum value. This can be achieved by making each of the input amplifier device and the output amplifier include a bias voltage control circuit. Use of such bias control circuits is, however, objectionable because the amplifier circuit becomes expensive.